Intraoperative neurophysiological monitoring system

ABSTRACT

A surgical system kit is described. The surgical system kit includes a peripheral electrode, a surgical access instrument configured to be placed in a surgical target site, and a control unit. The surgical access instrument has a body with a proximal end, and a distal end, two or more electrodes on the distal end at fixed locations and spaced apart a known distance. The control unit is configured to send a signal to the peripheral electrode, receive information indicative of a neural response from at least one electrode of the surgical access instrument, and interpret the information according to a nerve conduction velocity modality to measure the nerve conduction velocity through the segment of the nerve.

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BACKGROUND

Intraoperative neurophysiological monitoring is a continually evolvingfield that aims to localize and monitor neural structures according totheir functional basis within a human patient and, ultimately, it seeksto preserve the structural integrity of these neural structures duringsurgery or other invasive procedures. During spinal surgery for example,several neural structures may be placed at risk for potentialinjury—e.g., the spinal cord, one or more nerve roots, the lumbarplexus, and many (if not all) relevant vascular supply members going toand from the aforementioned elements.

Several electrophysiological modalities are currently available formonitoring various aspects of the central and peripheral nervous systemduring surgery or other invasive procedures in order to maintain theirstructural and/or functional integrity. Each neural monitoring modalityoffers a unique set of benefits and limitations as well as offeringvarying degrees of sensitivity or specificity as diagnostic techniques.For example, the most frequently used neural monitoring modalities forspinal procedures are SSEPs, MEPs, freerun or spontaneous EMG (sEMG),and triggered EMG (tEMG). In order to optimally preserve or protect theneural structures from structural or functional damage during spinalsurgery, an interdisciplinary effort among the surgical,neuromonitoring, and neuroanesthesia teams is imperative.

Beyond the acquisition and communication of data required forintraoperative monitoring lies the art and science of interpreting thenumerous permutations of results offered by multimodality intraoperativeneuromonitoring, during a wide variety of spine surgeries. Oftentimes itis the interpretation and correlation of this data with particularstructural or functionality impingements that is of the most benefit tothe surgeon and, ultimately, the health of the patient. It has beenfound, however, that consistent and reliable interpretation of multiplemodalities of information has been lacking and the structural andfunctional functioning of the patient's neural system has been impingedupon.

To that end, a need exists in the prior art for a neurophysiologicalmonitoring system which monitors the neural pathology of a patientduring an operation, interprets the data of multiple modalities ofinformation being aggregated through such neural monitoring, andcommunicates such interpreted information to the surgeon and/or othersin the operating chamber in a reliable and consistent manner. It is tosuch a neurophysiological monitoring system that the presently disclosedand claimed inventive concept(s), process(es), methodology(ies) and/oroutcome(s) is directed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Like reference numerals in the figures represent and refer to the sameor similar element or function. Implementations of the disclosure may bebetter understood when consideration is given to the following detaileddescription thereof. Such description makes reference to the annexedpictorial illustrations, schematics, graphs, drawings, and appendices.

FIG. 1 is a perspective view of a surgical system for intraoperativeneuromonitoring of at least one neural pathology throughout at least aportion of a surgical procedure according to the present disclosure.

FIG. 2 is a block diagram of the surgical system shown in FIG. 1.

FIGS. 3-16 show exemplary embodiments of status screens generated by acontrol unit of the surgical system of FIG. 1 in which multiple neuralmonitoring modalities are simultaneously being monitored in accordancewith the present disclosure.

FIG. 3 shows an exemplary status screen generated by the control unit ofthe surgical system of FIG. 1 in accordance with the presently disclosedconcepts.

FIG. 4 shows an exemplary baseline status screen generated by thecontrol unit of the surgical system of FIG. 1 in accordance with thepresent disclosure in which all monitored neural monitoring modalitiesare acceptable.

FIG. 5 shows an exemplary baseline status screen generated by thecontrol unit of the surgical system of FIG. 1 in which two of themultiple neural monitoring modalities (e.g., Train of Fours (TOF); andelectromyography (EMG)) are indicated as being within an unacceptablerange of predetermined values while two of the neural monitoringmodalities (e.g., Motor Evoked Potentials (MEP) and somatosensory evokedpotential (SSEP)) are indicated as being within an acceptable range ofpredetermined values.

FIG. 6 shows an exemplary baseline status screen generated by thecontrol unit of the surgical system of FIG. 1 in which one of themultiple neuromonitoring modalities (e.g., the electromyography) isindicated as being within an unacceptable range of predetermined valueswhile the other neural monitoring modalities are indicated as beingwithin an acceptable range of predetermined values.

FIG. 7 shows an exemplary positioning status screen generated by thecontrol unit of the surgical system of FIG. 1 in which all of themultiple neural monitoring modalities are indicated as being within anacceptable range of predetermined values.

FIG. 8 shows an exemplary approach status screen generated by thecontrol unit of the surgical system of FIG. 1 in which all of themultiple neural monitoring modalities are indicated as being within anacceptable range of predetermined values.

FIG. 9 shows an exemplary access status screen generated by the controlunit of the surgical system of FIG. 1 utilized when a surgeon isaccessing a patient's spine with a surgical accessory; the access statusscreen having a nerve proximity screen generated by the control unit ofthe surgical system of FIG. 1 indicating that the surgical accessory iswithin a predetermined range of acceptable distances away from thepatient's nerves and the other neural monitoring modalities areindicated as being within an acceptable range of predetermined values.

FIG. 10 shows an exemplary access status screen generated by the controlunit of the surgical system of FIG. 1 having the nerve proximity screengenerated by the control unit of the surgical system of FIG. 1 issuing avisual and/or audible warning to indicate that the surgical accessory iswithin a predetermined range of acceptable distances away from thepatient's nerves, but in close proximity (i.e., closely outside oradjacent to an unacceptable range of predetermined distances) to avastus lateralis nerve and an anterior tibialis nerve.

FIG. 11 shows an exemplary access status screen generated by the controlunit of the surgical system of FIG. 1 having a nerve proximity screengenerated by the control unit of the surgical system of FIG. 1 issuingan audible and/or visual alert due to the surgical accessory beingwithin a predetermined range of unacceptable distances away from thepatient's nerves and, in particular, that the surgical accessory iswithin an unacceptable range of predetermined distances away from thevastus lateralis nerve and the anterior tibialis nerve.

FIG. 12 shows an exemplary dissecting status screen generated by thecontrol unit of the surgical system of FIG. 1 in which a surgicalaccessory such as a retractor is being utilized by the surgeon andshowing (via visual or audible indicia) that one of the multiple neuralmonitoring modalities is within a predetermined range of unacceptabledistances away from a neural structure—e.g., indicating the possibleintrusion of the surgical accessory into the vastus lateralis nerve, abiceps femoralis nerve, and/or the anterior tibialis nerve.

FIG. 13 shows an exemplary dissecting status screen generated by thecontrol unit of the surgical system of FIG. 1 in which a status summaryscreen of the multiple neural monitoring modalities indicates (viavisual or audible indicia) that (i) the SSEP, MEP, TOF, and NCV neuralmonitoring modalities are within an acceptable range of predeterminedvalues, (ii) the EMG is not within an acceptable range of predetermined,and (iii) a nerve status summary screen generated by the control unit ofthe surgical system of FIG. 1 indicates via an audible or visual indiciathat the surgical accessory is not within an acceptable predeterminedrange of distances away from a nerve. The exemplary dissecting statusscreen also indicates a visual warning to the user that the surgicalaccessory is not within an acceptable predetermined range of distancesaway from a nerve.

FIG. 14 shows an exemplary dissecting status screen generated by thecontrol unit of the surgical system of FIG. 1 in which all of themultiple neural monitoring modalities are indicated as being within anacceptable range of predetermined values.

FIG. 15 shows an exemplary trial/insertion screen generated by thecontrol unit of the surgical system of FIG. 1 in which all of themultiple neural monitoring modalities are indicated as being within anacceptable range of predetermined values.

FIG. 16 shows an exemplary supplemental/fixation status screen generatedby the control unit of the surgical system of FIG. 1 in which all of themultiple neural monitoring modalities are indicated as being within anacceptable range of predetermined values.

FIG. 17 is a flow chart illustrating a method for conducting thesurgical procedure utilizing the surgical system depicted in FIGS. 1 and2 according to the present disclosure.

FIG. 18 shows an exemplary patient marked with nerve conduction velocitystimulation/recording sites in accordance with the present disclosure.

FIG. 19 shows an exemplary surgical access instrument within a psoasmuscle being used for nerve conduction velocity measurement inaccordance with the present disclosure.

FIG. 20 shows another embodiment of an exemplary surgical accessinstrument within a psoas muscle being used for nerve conductionvelocity measurement in accordance with the present disclosure.

DETAILED DESCRIPTION OF INVENTIVE CONCEPT(S)

Before explaining at least one embodiment of the inventive concept(s)disclosed herein in detail, it is to be understood that the presentlydisclosed and claimed inventive concept(s), process(es),methodology(ies) and/or outcome(s) is not limited in its application tothe details of construction and the arrangement of the components orsteps or methodologies set forth in the following description orillustrated in the drawings. The presently disclosed and claimedinventive concept(s), process(es), methodology(ies) and/or outcome(s)disclosed herein is capable of other embodiments or of being practicedor carried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting the presentlydisclosed and claimed inventive concept(s), process(es),methodology(ies) and/or outcome(s) herein in any way. With respect toany reference—patent or otherwise—mentioned herein, such referenceshould be considered to be incorporated by reference herein in itsentirety as if set forth explicitly herein.

In the following detailed description of embodiments of the presentlydisclosed and claimed inventive concept(s), process(es),methodology(ies) and/or outcome(s), numerous specific details are setforth in order to provide a more thorough understanding of the presentlydisclosed and claimed inventive concept(s), process(es),methodology(ies) and/or outcome(s). However, it will be apparent to oneof ordinary skill in the art that the presently disclosed and claimedinventive concept(s), process(es), methodology(ies) and/or outcome(s)within the disclosure may be practiced without one or more of thesespecific details, by skipping one or more of these specific details, orby modifying or transforming one or more these specific details in amanner that would be apparent to one of ordinary skill in the art giventhe present disclosure and teachings. In other instances, well-knownfeatures have not been described in detail to avoid unnecessarilycomplicating the instant disclosure and teachings and the followingspecification should be construed as including all relevant and/or knowndetails or teachings that would be within the skill and knowledge of oneof ordinary skill in the art.

The presently disclosed and claimed inventive concept(s), process(es),methodology(ies) and/or outcome(s) disclosed herein are generallydirected to a neurophysiological monitoring system for use during spinesurgery. The neurophysiological monitoring system is connected to thepatient prior to spine surgery and permits a surgeon to monitor multipleneural monitoring modalities simultaneously during the entirety of thespine surgery—e.g., from patient positioning to final closure of thesurgical wound or access point. The presently disclosed and taughtneurophysiological monitoring system provides the surgeon withinformation regarding the status of various nerves or other neuralstructures within the patient as well as other information useful inobtaining a successful surgical outcome—e.g., positional informationindicating the distance between one or more surgical accessories and oneor more nerves which, when brought to the attention of the surgeon orother operating room participant, enhances the likelihood that thesurgical accessories do not interfere (structurally or functionally)with one or more of the patient's nerves or other neural structures. Theneurophysiological monitoring system will be described hereinafter inthe context of spinal surgery utilizing a direct lateral approach to apatient's lumbar spine (i.e., 90 degrees to an anterior-posterior planeextending through a patient). However, it is to be understood, and wouldbe understood by one of ordinary skill in the art given the presentdisclosure and teachings, that the presently disclosed and claimedinventive concept(s), process(es), methodology(ies) and/or outcome(s)are equally applicable to other types of surgeries, such asposterior-lateral spinal surgery, anterior-lateral spinal surgery,anterior spinal surgery, and posterior spinal surgery, for example.

As used herein, the terms “network-based,” “cloud-based” and anyvariations thereof, are intended to cover the provision of configurablecomputational resources on demand via interfacing with a computernetwork, with software and/or data at least partially located on thecomputer network, by pooling the processing power of two or morenetworked processors, for example.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed.

As used herein the notation “a-n” appended to a reference numeral isintended as merely convenient shorthand to reference one, or more thanone, and up to infinity, of the elements or features identified by therespective reference numeral (e.g., 134 a-n). Similarly, a letterfollowing a reference numeral is intended to reference an embodiment ofthe feature or element that may be similar, but not necessarilyidentical, to a previously described element or feature bearing the samereference numeral (e.g., 148, 148 a, 148 b, etc.). Such shorthandnotations are used for purposes of clarity and convenience only, andshould not be construed to limit the presently disclosed and claimedinventive concept(s), process(es), methodology(ies) and/or outcome(s) inany way, unless expressly stated to the contrary.

As used in the instant disclosure the terms “provide,” “providing” andvariations thereof as used herein comprise displaying, or providing fordisplay, a screen either by one or more control units or to one or morecontrol units by a host computer. The one or more control units mayinterface with a computer network and/or allow the one or more controlunits to obtain information from a host computer by sending and/orreceiving digital and/or optical signals via a computer networkinterface (e.g. an Ethernet port, a TC/IP port, an optical port, a cablemodem, and combinations thereof), for example.

Further, unless expressly stated to the contrary, “or” refers to aninclusive or and not to an exclusive use of the term “or.” For example,a condition A or B is satisfied by anyone of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

In addition, use of the term “a” or “an” are employed herein to describeelements and components of the embodiments herein. This is done merelyfor convenience and to give a general sense of the presently disclosedand claimed inventive concept(s), process(es), methodology(ies) and/oroutcome(s). This description should be read to include one or at leastone and the singular also includes the plural unless it is readilyapparent to one of ordinary skill in the art that it is meant otherwise.

Finally, as used herein any reference to “one embodiment” or “anembodiment” means that a particular element, feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the presently disclosed and claimedinventive concept(s), process(es), methodology(ies) and/or outcome(s).The appearances of the phrase “in one embodiment” in various places inthe specification do not necessarily refer to the same embodiment unlessit would be readily apparent to one of ordinary skill in the art that itis meant otherwise.

Neural Monitoring Modalities

As one skilled in the art will understand and appreciate given thepresent disclosure and teaching(s), a variety of neural monitoringmodalities exist to monitor and communicate (either audibly, visually,or a combination thereof) to one or more persons the structural orfunctional status or location of a nerve or other neural structure. Theterm “modality,” as used herein, specifically refers to a physical agentwhich is applied to a patient in order to elicit a response from thepatient wherein the response provides information that allows a surgeon,for example, to determine information relating to the structural orfunctional status of a patient's nerves or other neural structures. Thephysical agent can be in the form of electricity, energy from magneticcoils, or outside physical stimulus such as physically moving thepatient or providing external force or movement, for example. Theinformation elicited by the response can include, for example, theproximity of a nerve to a surgical access instrument or other device,the direction of a nerve relative to the placement of a surgical accessinstrument or other device, nerve pathology assessments such as thehealth or functional state of the nerve, or even the state of anesthesiathat the patient is experiencing at the time of the application of thephysical agent. As discussed below, the neurophysiological monitoringsystem may use a variety of different types of neural monitoringmodalities such as somatosensory evoked potential, triggeredelectromyography, spontaneous electromyography, motor evoked potentials,train of fours (which may be referred to herein as a “twitch test”) andnerve conduction velocity. Various types of neural monitoring modalitieswill be discussed hereinafter in more detail.

Somatosensory Evoked Potential

As used herein, the term “SSEP” stands for somatosensory evokedpotential. Somatosensory evoked potentials provide monitoring of thedorsal column-medial lemniscus pathway, which mediates tactilediscrimination, vibration sensation, form recognition, and joint/musclesensation (conscious proprioception). Receptors in the skin, tendons,and muscles generate information that corresponds to these primarysensory modalities and relay these signals to neurons whose soma arelocated in dorsal root ganglia at all spinal levels. Axons from thesefirst-order neurons project to the spinal cord via the medial root entryzone, giving rise to the fasciculi gracilis and cuneatus, whichsubsequently carry sensory information from the lower and upperextremities, respectively. The first synapse in this pathway occurs inthe lower medulla after these tracts ascend via the dorsal columns inthe spinal cord. Following a decussation that occurs at the medullarylevel, the medial lemniscus is formed; it ascends to the thalamus andultimately relays sensory information to the primary somatosensorycortex (Brodmann areas 3, 1, and 2). Since SSEPs monitor the dorsalcolumn-medial lemniscus pathway, standard patient sensory examinationfor tactile discrimination, vibration sensation, and joint/musclesensation (conscious proprioception) is recommended prior to surgery, todocument any deficits that may limit intraoperative neuromonitoring.

In the upper extremities, the median nerve (C-6, C-7, C-8, and T-1roots) and ulnar nerve (C-8 and T-1) are frequently selected formonitoring, whereas the posterior tibial nerve (L-4, L-5, S-1, and S-2)and peroneal nerve (L-4, L-5, and S-1) are typically used in the lowerextremities. Somatosensory evoked potentials involve electricalstimulation of mixed sensory and motor fibers caudal to the region ofthe spinal cord at risk, paired with recording of these signals rostralto the region at risk (typically at the dorsal neck and scalp).Electrical stimulation in the extremities produces major positive andnegative deflections as signals ascend via the somatosensory pathway.Most often, a negative potential is measured at the scalp correspondingto the upper extremities at 20 milliseconds (N20), and a positivepotential is measured at the scalp corresponding to the lowerextremities at 37 milliseconds (P37). Additional subcortical waveformscan be obtained intraoperatively as the electrical volley propagatesthrough the somatosensory pathway. A peripheral response recorded at thelevel of the brachial plexus (for the upper extremities) or thepopliteal fossa (for the lower extremities) can be performed toascertain adequacy of stimulation. These peripheral responses can alsohelp to detect peripheral limb ischemia or nerve compression. It isimportant to note that in the case of SSEPs, these earlier peaks tend tobe less sensitive to anesthesia, and can therefore frequently be used todifferentiate SSEP monitoring changes resulting from anesthetic effectsfrom those relating to surgical manipulation.

Alarm criteria of a 50% reduction in amplitude and/or a 10% increase inlatency are generally used as guidelines for notifying the surgeon of apotential deficit, and corrective intervention should be considered ifthese changes correspond to a particular surgical manipulation. Factorsthat potentially affect the SSEP amplitude include halogenated agents,nitrous oxide, hypothermia, hypotension, and electrical interference. Acommon factor affecting SSEP latency readings is temperature. Any SSEPchanges with amplitude reduction of more than 50% should also beconsidered relevant if they are temporally associated with a specificsurgical intervention, such as during placement of spinalinstrumentation or during correction of a spinal deformity.

Although SSEP signals are good basic indicators of spinal cord function,less information is provided regarding nerve root function.Somatosensory evoked potentials are a composite of summated neuralsignals that enter the spinal cord through multiple segments. Inaddition, due to central amplification, it is possible for SSEPs toremain completely normal in the face of a nerve root injury.

Motor Evoked Potentials

As used herein, the term “MEP” refers to Motor Evoked Potentials. Motorevoked potentials (MEP) are recorded from muscles following directstimulation of exposed motor cortex, or transcranial stimulation ofmotor cortex, either magnetic or electrical. Transcranial magnetic MEP(TCmMEP) potentially offer clinical diagnostic applications.Transcranial electrical MEP (TCeMEP) has been used widely forintraoperative monitoring of pyramidal tract functional integrity andwould be understood readily by one of ordinary skill in the art.

For standard transcranial MEP recording (TcMEP), stimulation electrodesare placed at C3 and C4 (10-10 according to the International System ofindication) for activation of both upper and lower extremity musclegroups, with alternative sites at C1 and C2 if more focal activation ofthe lower extremity muscle groups is desired. Establishing a patientsetup with multiple sites available for stimulation is recommended,especially in patients with myelopathy, given the greater difficulty inobtaining MEP recordings. The stimulation intensity alters the currentfield size and distribution to the cortex and subcortical fibers.Increasing stimulation intensity correlates with greater axonalrecruitment and spatial summation along with bilateral stimulation.Subcortical white matter motor tracts are activated at the bend of theaxon exiting the gray matter, or entering the internal capsule or evenbrainstem, which is not an issue when the structures at risk are locatedbelow the foramen magnum, as is the case in spine surgery. Stimulationtrains increase temporal summation at the α-motoneurons, leading to ahigher likelihood of achieving a stimulus threshold. Stimulationrates >200 Hz are typically required for temporal summation atmotoneurons. Latencies of 20 msec in the hand and 45 msec in the footare typically observed, depending on various factors such as theunderlying pathological condition, the patient's height, and bodytemperature.

There are a variety of methods utilized for the interpretation of MEPs.For example, four methods are routinely used for interpretation forTcMEP responses: 1) the all-or-nothing criterion, 2) the amplitudecriterion, 3) the threshold criterion, and 4) the morphology criterion.The all-or-nothing criterion may be the most widely cited and usedmethod, given the inherent variability of signals in MEP monitoring.Based on this approach, a complete loss of the MEP signal from apreliminary baseline recording is indicative of a clinically significantevent. A modification of the all-or-nothing approach involves measuringthe CMAP (“compound muscle action potential”) amplitude at baseline,then measuring relative changes in amplitude to determine if aclinically significant change has occurred. For example, an 80%amplitude decrement in at least 1 out of 6 recording sites may be usedas a criterion for a clinically significant change. A similar form ofreasoning can be applied to the threshold criterion, which analyzes theincreases in stimulation threshold required to maintain CMAP responses.Lastly, the morphology criterion looks at impaired motor conduction ofthe corticospinal tracts by tracking changes in the pattern and durationof MEP waveform morphology. Factors that may alter MEP waveformmorphological characteristics include anesthetic fade, body temperature,blood pressure, surgical positioning, and technical pitfalls, amongothers.

Although MEPs have become commonplace for neuromonitoring of the motortracts, there are some disadvantages to MEP monitoring. Primary amongthe many drawbacks of MEP monitoring is the inability of MEP to performcontinuous monitoring (which can be accomplished with SSEPs), requiringthat MEPs be obtained intermittently at given intervals during thesurgery. Another inherent limitation of monitoring MEP signals is thatthey may be more technically challenging to obtain and/or properlyinterpreting the signals during complicated surgical procedures.

Spontaneous Electromyography

As used herein, sEMG refers to “spontaneous electromyography” (alsogenerally known in the art as “free run” electromyography) which can beused to intraoperatively monitor the corresponding nerve rootsresponsible for muscle innervation. This spontaneous motor activity canbe measured with recording electrodes placed in the muscles of interestand based on the structures at risk. Although no stimulation isperformed for this technique, surgical manipulation such as pulling,stretching, or compression of nerves produces neurotonic dischargesresulting in activity in the corresponding innervated muscle(s).Specific muscles are normally paired with single nerve roots, yet inreality some redundancy in innervation occurs, and muscle selection ismade to maximize coverage based on the spinal level of interest to thesurgeon. During cervical spine procedures, the C-5 nerve root is atparticular risk of injury and requires particular attention inmonitoring. For this reason, concurrent monitoring of 2 muscles isoftentimes recommended to minimize the risk of C-5 nerve root injury.The deltoid (predominantly C-5, also C-6) and biceps brachii(predominantly C-6, also C-5) muscles may be used to monitor the C-5level. Spontaneous EMG tends to be quite sensitive to irritation of thenerve root due to retraction, irrigation, and manipulation duringsurgery.

Triggered Electromyography

Over the past 20 years, segmental instrumentation and fusion usingpedicle screw constructs have become the standard for spinalstabilization. A potentially preventable risk of pedicle screw placementis a medial screw breach of the pedicle wall into the spinal canal.Triggered EMG is a method that can be used to determine whether screwshave breached the medial or inferior pedicle wall and thus pose a riskto the exiting nerve root at that level. When a pedicle screw isaccurately placed, the surrounding bone acts as an insulator toelectrical conduction, and a higher amount of electrical current is thusrequired to stimulate the surrounding nerve root. Typically, a monopolarelectrode is used to directly stimulate the top of the pedicle screw atincreasing current intensities. Needle electrodes in the appropriatemuscle groups measure CMAP time locked to the stimulation. In order toensure that the stimulus current is delivered correctly, direct nerveroot stimulation using <2 mA can be attempted to ensure a CMAP responsein the appropriate distal muscle group and thereby confirm the deliveryor application of the stimulus current.

When a medial pedicle wall breach occurs, the stimulation threshold issignificantly reduced. Due to the variation in thickness and shapebetween thoracic and lumbar pedicles, different stimulation thresholdsexist for these regions. Earlier studies have demonstrated that athreshold <10 mA for screw stimulation, or 7 mA for probe stimulation,suggest a medial wall breach in the lumbar pedicles. A thresholdresponse between 10 and 20 mA gives a reasonable probability that no ofbreach of the medial wall has occurred, whereas thresholds >15 mAindicate a 98% likelihood of accurate screw positioning on postoperativeCT scan. Thresholds above 20 mA assure a strong probability that thereis no breach of the medial pedicle wall. For thoracic pedicle screwplacement, stimulation thresholds <6 mA suggest a medial pedicle breach.

During pedicle screw stimulation, false-negative responses can occur asa result of various factors, including the use of muscles relaxants,current spread, or preexisting nerve damage. The degree of musclerelaxation can be measured using a train-of-4 test. Just as in the caseof sEMG monitoring, tEMG monitoring requires that no paralytics be usedand that 4 of 4 twitches are optimal for reliable recording. Specialattention should to be paid to fluid, blood, or soft tissue around thehead of the screw at the time of stimulation that could potentiallyshunt current away from the screw. Furthermore, it is important that thestimulation probe be placed directly on the top of the screw and not thetulip, as these 2 structures are not structurally fused and therefore donot conduct current as a single unit. Once the probe is placed on thescrew, current will ideally flow from the screw to an appropriatelyplaced reference electrode in the paraspinal muscles on thecontralateral side. A third possible reason for false-negativethresholds is the presence of preexisting nerve root injury. Injurednerve roots will have higher triggering thresholds, with literaturereports ranging from 6 to >10 mA for a chronically compressed root, ascompared with 2 mA for a normal nerve root. In nerve roots where thereis known or suspected damage, direct nerve root threshold testing isvaluable to establish a baseline value.

Train of Fours

A train of fours analysis can be utilized to quantify the amount ofparalytic in a patient to determine a state of anesthesia that thepatient is experiencing at the time of testing. In a train of foursanalysis, four electrical stimuli are typically presented to thepatient's peripheral nerves resulting in four twitches in thecorresponding muscle groups. The strength of the muscle twitchescorresponds to the quantity/amount of paralytic within the patient. Inother words, an amplitude of the response correlates to a level of thepatient's paralysis. As will be discussed in more detail below, a trainof fours analysis is preferably performed prior to every major surgicalevent so that the surgeon will be informed of the patient's level ofparalysis or level of anesthesia. When the surgery is directed to thepatient's spine, common major surgical events include access, dilation,retraction, and the like.

Nerve Conduction Velocity

Nerve conduction velocity (NCV) is a test to determine how “fast”electrical signals are capable of moving through a nerve at the time oftesting. The nerve conduction velocity test is implemented by attachingsurface electrodes on the skin over nerves at various locations. Eachsurface electrode gives off a very mild electrical impulse, whichstimulates the nerve. The nerve's resulting electrical activity isthereafter recorded by the other electrodes. The distance betweenelectrodes and the time it takes for electrical impulses to travelbetween electrodes is used to determine the speed of the nerve signals.It should be noted that electromyography (recording from needles placedinto the muscles) may be performed at the same time as nerve conductionvelocity tests.

NCV may involve the stimulation of peripheral nerves using surfaceelectrodes placed along a nerve path within a patient. In particular,stimulating and recording electrodes may be placed along the nerve path,in addition to a ground electrode placed nearby. The recordingelectrode, placed along the nerve path, may be placed on the nerve pathas it leads proximally away from a limb. The electrodes placed on thepatient may be measured to correlate the time of nerve conduction into avelocity measurement. NCV may differ from patient to patient, but may bein the range of 45-55 meters per second. The determination of amplitudeand latency may also be used during NCV measurements. Nerve healthmonitoring via NCV may be used in addition to other nerve monitoringprocedures during the creation and maintenance of a spinal accesscorridor, during a spinal surgery, whether from an anterior, posterior,anterolateral, posterolateral, or lateral approach.

NCV may compliment triggered and running EMG measurements. While EMGprimarily measures motor nerve activity, NCV primarily measures sensorynerve activity. NCV may be utilized to measure conduction in eitherdirection along the nerve's path, orthodromic or antidromic. During aspinal access surgical procedure, EMG may measure the direct stimulationof a nerve or nerve root that is accessible in the surgical field, witha mono or bipolar probe. Stimulus evoked CMAPs (Compound Muscle ActionPotentials) which appear normal may demonstrate integrity of thefunctional nerve muscle unit. If a root or nerve supplying a monitoredmyotome is manipulated during the surgical procedure, the muscledischarges and resultant motor unit potentials may be recorded. Thesepotentials quickly diminish. If a nerve is severed, loses its ability todischarge due to traction, compression, or ischemia, EMG may losediagnostic value. In such cases, NCV may better indicate a nerve'shealth. NCV may also be used to verify a nerve's health if the desiredoutcome is to relieve a pinched nerve via decompression or surgicalintervention. Further, NCV measurements may not be affected by generalanesthesia and neuromuscular blocking agents, as opposed to EMG whichmay not be possible with complete neuromuscular blocking.

NCV may be used to measure the nerve conduction of motor nerves andsensory nerves. Motor nerve conduction velocity (mNCV) measurement maybe measured by transcranial stimulation, with a nerve path extending,for example, from the brain to spinal cord to lumbar plexus toretractor. It may be necessary to record baseline data as NCVmeasurements are patient specific due to changes in patient height,weight, age, etc. Sensory nerve conduction velocity (sNCV) measurementmay be measured by stimulating a peripheral nerve at around 25 mA atabout 4-5 Hz, with a nerve path which may be from a limb to lumbarplexus to retractor. As with mNCV, it may be necessary to recordbaseline data as the sNCV measurements are patient specific due tochanges in patient height, weight, age, etc. The mNCV and sNCVmeasurements can verify nerve traction, compression, ischemia, orimpairment in motor nerves and sensory nerves, respectively. If anysignificant NCV change is presented, the NCV change may indicatetemporary nerve impairment that may be alleviated by repositioning ofthe surgical access instrument impinging the nerve during surgery.

As will be appreciated by one of ordinary skill in the art provided theteachings and disclosure herein, various additional modalities may beincorporated within the surgical system disclosed and claimed herein.For example, but not by way of limitation, mechanomyography (MMG) may beemployed as one such neural monitoring modality. MMG systems function bymeasuring the mechanical response of a muscle following nervestimulation, compared to traditional techniques that monitor theelectrical response of muscle using EMG. MMG has been widely used inlaboratory settings to study things such as muscle fatigue and, giventhe present disclosure, one of ordinary skill in the art will appreciatethat MMG can be applied as an intraoperative tool for locating nerves.MMG is effective for detecting the presence of nerves or other neuralstructures during surgery—particularly with regards to minimallyinvasive surgical procedures—where the nerves or other neural structurescannot be directly visualized. Since EMG systems monitor for smallchanges in muscle electrical activity, there is the potential forelectrical interference when using EMG in certain circumstances. Byusing MMG, alone or in combination with EMG or other modalities,electrical interference issues are minimized or can be ignored since anyresponse of the muscles to the electrical stimulation is measuredthrough mechanical sensors such as accelerometers, for example but notby way of limitation. MMG may also provide faster response rates therebyindicating a higher sensitivity for detection of nerves at a lowerthreshold. Further, muscle response to electrical stimulus varies withthe distance of the nerve from the source of the stimulus: i.e., byworking with different levels of current, a relationship between thecurrent and distance is known thereby allowing the surgeon to determineprecisely how far a nerve is from the stimulus probe. In recent studies,MMG detected the presence of a nerve on average 1.2 seconds earlier thanEMG, using approximately half the amount of stimulating current. Sinceelectrical resistance is highly variable, depending on the conductingtissue, EMG may require currents as high as 200 mA while MMG in similartissue would only require, for example, a maximum current output of 6mA.

Given the preceding—as well as the knowledge known—one of ordinary skillin the art would appreciate that a surgical system could incorporateone, two, three and up to an infinite number of different neuralmonitoring modalities capable of employing nerve proximity, nervedirection, and nerve pathology assessments according to the presentlydisclosed and claimed inventive concept(s), process(es),methodology(ies) and/or outcome(s). It should be understood that thenumber of neural monitoring modalities used and communicated to asurgeon or other operating room personnel (e.g., by visual, aural orolfactory indicia) are not limited to a single neural monitoringmodality at any one particular time. Rather, one or more indicia can becommunicated at any given time—for example, EMG and NCV data may becommunicated to the surgeon or other operating room personnel at thesame time. Furthermore, all of the modalities may be communicated at thesame time. As will be even more apparent in light of the informationbelow, the presently disclosed and claimed inventive concept(s),process(es), methodology(ies) and/or outcome(s) encompass all suchvariations of neural monitoring modalities being represented to thesurgeon or other operating room personnel.

DESCRIPTION OF SURGICAL SYSTEM

FIG. 1 illustrates, by way of example only, a neurophysiologicalmonitoring system 8 having a surgical system 10 capable of employingnerve proximity, nerve direction, and nerve pathology assessmentsaccording to the presently disclosed and claimed inventive concept(s),process(es), methodology(ies) and/or outcome(s). As will be explained ingreater detail below, the surgical system 10 is capable of providingsafe and reproducible access to any number of surgical target sites, andwell as monitoring changes in nerve pathology (health or status) duringsurgical procedures. It is expressly noted that, although describedherein largely in terms of use in spinal surgery, the surgical system 10and related methods of the presently disclosed and claimed inventiveconcept(s), process(es), methodology(ies) and/or outcome(s) are suitablefor use in any number of additional surgical procedures wherein tissuehaving significant neural structures must be passed through (or near) inorder to establish an operative corridor, or where neural structures areretracted or otherwise impinged upon by surgical access instruments suchas dilators, retractors and the like.

The surgical system 10 includes a control unit 12, a patient module 14,an EMG harness 16, a return electrode 18 coupled to the patient module14, a plurality of peripheral nerve stimulation electrodes 19, a host ofsurgical accessories 20 capable of being coupled to the patient module14 via one or more accessory cables 22, and a multiple purpose unit 23capable of carrying out multiple modalities of stimulation shown in FIG.1 for example, but not by way of limitation, multiple purpose unit 23may be an evoked potential stimulator 23 connected to the patient module14 via one or more accessory cables 24. The surgical accessories 20 mayinclude, but are not necessarily limited to, surgical access components(such as a K-wire 25, one or more dilators 26, and a working dilator28), neural pathology monitoring devices (such as nerve root retractor30), and devices for performing pedicle screw test (such as screw testprobe 32). A block diagram of the surgical system 10 is shown in FIG. 2,the operation of which is readily apparent to one of ordinary skill inthe art in view of the following description. The one or more patientmodule 14 can be a separate component that is external to the base 38 ofthe control unit 12, or within the base 38 of the control unit 12.

The control unit 12 comprises one or more processors 12 a capable ofexecuting processor executable code, one or more non-transitory memory12 b capable of storing processor executable code, an input device 12 c,and an output device 12 d, all of which can be stand-alone, partially orcompletely network-based or cloud-based, and not necessarily located ina single physical location.

The one or more processors 12 a can be implemented as a single processor12 a or multiple processors 12 a working together to execute the logicdescribed herein. Exemplary embodiments of the one or more processor 12a include a digital signal processor (DSP), a central processing unit(CPU), a field programmable gate array (FPGA), a microprocessor, amulti-core processor, and combinations thereof. The one or moreprocessor 12 a is capable of communicating with the one or more memories12 b via a path 12 e which can be implemented as a data bus, forexample. The one or more processor 12 a is capable of communicating withthe input device 12 c and the output device 12 d via paths 12 f and 12g, respectively. Paths 12 f and 12 g may be implemented similarly to, ordifferently from, path 12 e. The one or more processor 12 a is furthercapable of interfacing and/or communicating with the one or more patientmodules 14 via a network 33, such as by exchanging electronic, digitaland/or optical signals via one or more physical or virtual ports using anetwork protocol such as TCP/IP, for example. The network 33 can also beimplemented with a serial and/or parallel cable utilizing any suitableprotocol. It is to be understood that in certain embodiments using morethan one processor 12 a, the one or more processor(s) 12 a may belocated remotely from one another, located in the same location, orcomprising a unitary multi-core processor (not shown). The one or moreprocessor 12 a is capable of reading and/or executing processorexecutable code and/or or creating, manipulating, altering, and storingcomputer data structures into the one or more memory 12 b.

The one or more memory 12 b stores processor executable code for causingthe one or more processor 12 a to implement the functions describedherein. The one or more memory 12 b may be implemented as anyconventional non-transitory memory 12 b, such as random access memory(RAM), a CD-ROM, a hard drive, a solid state drive, a flash drive, amemory card, a DVD-ROM, a floppy disk, an optical drive, a compact flashdrive, holographic drives, and combinations thereof, for example. It isto be understood that while one or more memory 12 b is shown located inthe same physical location as the processor 12 a, the one or more memory12 b may be located remotely from the processor 12 a and may communicatewith the one or more processor 12 a via the network 33 a, or a network33 b. Additionally, when more than one memory 12 b is used, one or morememory 12 b may be located in the same physical location as theprocessor 12 a, and one or more memory 12 b may be located in a remotephysical location from the processor 12 a. The physical location(s) ofthe one or more memory 12 b can be varied, and the one or more memory 12b may be implemented as a “cloud memory” i.e., one or more memory 12 bwhich is partially, or completely based on or accessed using thenetworks 33 a or 33 b.

The input device 12 c transmits data to the processor 12 a, and can beimplemented as a keyboard, a mouse, a touch-screen, a camera, a cellularphone, a tablet, a smart phone, a PDA, a microphone, a network adapter,a probe having a sensor therein, a microcapillary testing device orarray, a microfluidic testing device, and combinations thereof, forexample but not by way of limitation. Any device capable of functionallytransmitting data to the processor 12 a can be used as the input device12 c. The input device 12 c may be located in the same physical locationas the control unit 12, or may be remotely located and/or partially orcompletely network-based. The input device 12 c communicates with theprocessor 12 a via path 12 f.

The output device 12 d transmits information from the processor 12 a toa user, such that the information can be perceived by the user. Forexample but not by way of limitation, the output device 12 d can beimplemented as a server, a computer monitor, a cell phone, a tablet, aspeaker, a website, a PDA, a fax, a printer, a projector, a laptopmonitor, and combinations thereof. The output device 12 d can bephysically co-located with the processor 12 a, or can be locatedremotely from the processor 12 a, and may be partially or completelynetwork based (e.g., a website). The output device 12 d communicateswith the processor 12 a via the path 12 g. As used herein, the term“user” is not limited to a human, and may comprise a human using acomputer, a host system, a smart phone, a tablet, a computerized pen orwriting device, and combinations thereof, for example but not by way oflimitation.

In one embodiment, the control unit 12 includes a touch screen display36 and a base 38. In this embodiment, the touch screen display 36 formsthe input device 12 c and the output device 12 d. The touch screendisplay 36 is preferably equipped with a graphical user interface (GUI)capable of communicating information to the user and receivinginstructions from the user. The base 38 preferably forms a housingcontaining computer hardware and software implementing the processor 12a and the non-transitory memory 12 b to control the stimulation sources,receive digitized signals and other information from the patient module14, and processes the neural monitoring modalities, such as anelectro-myocardial graph, to extract characteristic information for eachmuscle group, and displays the processed data to the operator via thetouch screen display 36. The primary functions of the software stored onthe one or more memory 12 b of the control unit 12 include receivinguser commands via the touch screen display 36, activating stimulation ina requested mode of the available surgery modes (e.g., baseline,positioning, approach, access, dissecting, trial/insertion andsupplemental fixation), processing signal data according to definedalgorithms stored on the memory 12 b, displaying received parameters andprocessed data, and monitoring system status and reporting faultconditions.

The patient module 14 is connected to the control unit 12 via thenetwork 33 a which may be a parallel or serial cable and contains theelectrical connections to all electrodes, signal conditioning circuitry,stimulator drive and steering circuitry, and a digital communicationsinterface to the control unit 12. In use, the control unit 12 may besituated outside but close to the surgical field (such as on a cartadjacent the operating table) such that the touch screen display 36 isdirected towards the surgeon for easy visualization. The patient module14 may be located between the patient's legs, or may be affixed to theend of the operating table at mid-leg level using a bedrail clamp. Theposition selected should be such that the leads can reach their farthestdesired location without tension during the surgical procedure.

Referring now to FIG. 3, the information displayed to the user on touchscreen display 36 may include, but is not necessarily limited to,alpha-numeric and/or graphical information regarding nerve proximity,nerve direction, nerve pathology, stimulation level, myotome/EMG levels,screw testing, advance or hold instructions, the instrument in use and alevel of the patient's paralysis. Shown in FIG. 3 is a system statusscreen 58 displayed, for example, when the surgeon system 10 has beenplaced into the system status mode. In one embodiment (set forth by wayof example only) the system status screen 58 provided by the touchscreen display 36 includes the following components:

1) a mode section 60 including a plurality of interfaces 62 a-h that canbe selected by a user to place the surgeon's system 10 in a variety ofpredetermined modes. The predetermined modes can vary and are shown byway of example in a situation where the surgeon's system 10 is used fora direct lateral approach to the patient's lumbar spine. In thisexample, the predetermined modes include a status mode, a baseline mode,a positioning mode, an approach mode, an access mode, a dissecting mode,a trial/insertion mode and a supplemental fixation mode. Depending uponthe mode, the interface 62 a-h may include an identification of thesurgical accessory 20 to be used in the mode, such as the surgicalaccess components (K-Wire, Dilators, Working Dilator), nerve pathologymonitoring device (Nerve Root Retractor), and/or screw test device(Screw Test Probe) depending on which is attached.

2) a status summary section 66 including a plurality of zones indicatinga current status for each of the neural monitoring modalities, which inthe example shown in FIG. 3 includes SSEP, MEP, TOF, EMG and NCV. Ingeneral, the current status can vary, but in an embodiment, the currentstatus can either be within a predetermined range that is consideredacceptable, unacceptable or on the peripheries of these areas and thusconstitutes a warning zone indicating that the user should be cautiousin preceding with the task being undertaken. The current status can becommunicated in a variety of ways, such as by changing colors of thezones, flashing lights, voice prompts or audio warnings, pleasant ornoxious smells, or the like. In a one embodiment, the color green isutilized to communicate that the status is within a predetermined rangeof acceptability, the color red is utilized to communicate that thestatus is within a predetermined range of unacceptability, and the coloryellow is utilized to communicate that the status is within apredetermined range indicating that a warning is necessary.

3) an anesthetic status section 72 providing a status of the patient'sparalysis. Data regarding the status of the patient's paralysis can bedetermined utilizing a train of four analysis, for example, having foursensors connected to the patient's nerves as discussed above. For thisreason, the anesthetic status section 72 may be referred to herein as atrain of four status. In the example shown, the anesthetic statussection 72 includes separate zones 74 a, 74 b, 74 c and 74 d with one ofthe zones for the sensors connected to the patient's nerves. As shown,each of the zones 74 a, 74 b, 74 c and 74 d may show a magnitude oftwitch generated by the electrical signals used in the train of fouranalysis.

4) a monitoring location status section 80 providing an image 82 of ahuman body/skeleton showing the electrode placement on the body, nervesupon which the electrodes are placed and EMG status 84 a-j of waveformsbeing sensed by the electrodes. Exemplary nerves that may be monitoredby EMG and indicated in status 84 a-j include Iliacus/Obductor, VastusMedialis, Vastus Lateralis, Biceps Femoralis, and Anterior Tibialis, forexample but not by way of limitation.

The surgical system 10 accomplishes safe and reproducible access to asurgical target site by detecting the existence of (and optionally thedistance and/or direction to) neural structures before, during, andafter the establishment of an operative corridor through (or near) anyof a variety of tissues having such neural structures which, ifcontacted or impinged, may otherwise result in neural impairment for thepatient. The surgical system 10 does so by electrically stimulatingnerves via one or more stimulation electrodes at the distal end of thesurgical access components 25-28 while monitoring the EMG responses ofthe muscle groups innervated by the nerves. In one embodiment, this isaccomplished via 8 pairs of EMG electrodes 34 placed on the skin overthe major muscle groups on the legs (four per side), an anode electrode35 providing a return path for the stimulation current, and a commonelectrode 37 providing a ground reference to pre-amplifiers in thepatient module 14.

In use, all appropriate electrodes including the return electrode 18,peripheral nerve stimulation electrodes 19, motor evoked potentialstimulator 23, EMG electrodes 34, the anode electrode 35 and the commonelectrode 37 are applied to the patient prior to positioning. Thepatient is positioned in a lateral decubitus position, and then acorrect operative level and incision location is located, preferablywith fluoroscopic views, and thereafter a skin incision targeting aninterior third of an intravertebral disc space is made. However, alongitudinal incision may be used if multiple levels will be fused, forexample.

Once the skin incision is made and the subcutaneous tissue is takendown, the oblique muscles of the abdomen should be visible. The surgicalaccess components 25-28 are designed to bluntly dissect the tissuebetween the patient's skin and the surgical target site through theoblique muscles, the retroperitoneal space, and the psoas muscle to formthe operative corridor to the patient's spine. The operative corridor isformed by advancing the K-wire 25, or an initial dilator 26, towards thetarget site, preferably after having been aligned using any number ofcommercially available surgical guide frames. The K-wire 25 and/or theinitial dilator 26 can be provided with one or more stimulatingelectrodes that emit electricity in order to aid in determining theposition of the K-wire 25 and/or the initial dilator 26 relative to oneor more of the patient's nerves and/or other neural structures.

An obturator (not shown) may be included inside the initial dilator 26and may similarly be equipped with one or more stimulating electrodes.Once the proper location is achieved, the obturator (not shown) may beremoved and the K-wire 25 inserted down the center of the initialdilator 26 and docked to the given surgical target site, such as theannulus of an intervertebral disc. Dilators of increasing diameter arethen guided over the previously installed dilator 26 until the desiredlumen is installed. By way of example only, the dilators 26 may range indiameter from 6 mm to 30 mm. In one embodiment, each dilator 26 has astimulating electrode at the tip to allow detection and directionevaluation, as will be described below. In another embodiment, eachdilator 26 may have more than one stimulating electrode placed at thetip or along the side of each of the dilators 26. The working dilator 28is installed over the last dilator 26 and then all the dilators 26 areremoved from inside the inner lumen of the working dilator 28 toestablish the operative corridor therethrough.

A stimulator driver 42 is provided to electrically couple the particularsurgical access component 25-28 to the patient module 14 (via accessorycable 22). In one embodiment, the stimulator driver 42 includes one ormore buttons for selectively activating the stimulation current and/ordirecting it to a particular surgical access component.

The surgical system 10 accomplishes neural pathology monitoring byelectrically stimulating a retracted nerve root via one or morestimulation electrodes at the distal end of the nerve root retractor 30while monitoring the EMG responses of the muscle group innervated by theparticular nerve. The EMG responses provide a quantitative measure ofthe nerve depolarization caused by the electrical stimulus.

Analysis of the EMG responses may then be used to assess the degree towhich retraction of a nerve or other neural structure affects the nervefunction over time, as will be described with greater particularitybelow. One advantage of such monitoring, by way of example only, is thatthe conduction of the nerve may be monitored during the procedure todetermine whether the neurophysiology and/or function of the nervechanges (for the better or worse) as the result of the particularsurgical procedure. For example, it may be observed that the nerveconduction increases as the result of the operation, indicating that thepreviously inhibited nerve has been positively affected by theoperation. The nerve root retractor 30 may comprise any number ofsuitable devices capable of maintaining contact with a nerve or nerveroot. The nerve root retractor 30 may be dimensioned in any number ofdifferent fashions, including having a generally curved distal region(shown as a side view in FIG. 1 to illustrate the concave region wherethe nerve will be positioned while retracted), and of sufficientdimension (width and/or length) and rigidity to maintain the retractednerve in a desired position during surgery. The nerve root retractor 30may also be equipped with a handle 31 having one or more buttons forselectively applying the electrical stimulation to the stimulationelectrode(s) at the end of the nerve root retractor 30. In oneembodiment, the nerve root retractor 30 is disposable and the handle 31is reusable and autoclavable.

FIG. 4 shows an exemplary baseline status screen 90 in accordance withthe present disclosure in which all monitored neural monitoringmodalities are within the range of predetermined values indicating thatthe location of the surgical device is acceptable. The baseline statusscreen 90 is similar to the system status screen 58 which was discussedpreviously with reference to FIG. 3.

FIG. 5 shows an exemplary baseline status screen 94 in which two of themultiple neural monitoring modalities (e.g., Train of Fours (TOF); andelectromyography (EMG)) displayed within the status summary section 66are indicated as being within the predetermined range of valuesindicating an interpretation of being unacceptable while two of theneural monitoring modalities (e.g., Motor Evoked Potentials (MEP) andsomatosensory evoked potential (SSEP)) are indicated as being within thepredetermined range of values indication an interpretation of beingacceptable. Further, an alert is being issued within the anestheticstatus section 72 indicating that the level of twitch being sensed byone of electrodes is below the predetermined range of values indicatingacceptability. In addition, the monitoring location status section 80indicates levels being within the predetermined range of valuesindicating unacceptability are being sensed with respect to thepatient's left vastus lateralis nerve, and the patient's left anteriortibialis nerve. The levels shown as being outside the acceptable rangeof predetermined values may be visualized by utilizing red waveformwindows and myotome red highlighting.

FIG. 6 shows an exemplary baseline status screen 96 in which one of themultiple neural monitoring modalities (e.g., the electromyography) isindicated as being within a predetermined range of values indicating anunacceptable reading while the other neural monitoring modalities withinthe status summary section 66 are indicated as being within apredetermined range of values indicating an acceptable reading. Inaddition, the monitoring location status section 80 indicates beingwithin a predetermined range of values indicating that unacceptablelevels are sensed with respect to the patient's left anterior tibialisnerve.

FIG. 7 shows an exemplary positioning status screen 100 in which all ofthe multiple neural monitoring modalities are indicated as being withina predetermined range of values indicating an acceptable reading. Thisis shown for example by utilizing green check marks within the statussummary section 66, an absence of red within the anesthetic statussection 72, and green waveforms utilized within the monitoring locationstatus section 80.

FIG. 8 shows an exemplary approach status screen 104 in which all of themultiple neural monitoring modalities are indicated as being within apredetermined range of values indicating an acceptable reading. Theapproach status screen 104 is provided when the surgeon system 10 isplaced into the approach mode before the surgeon forms an incisionwithin the patient to provide access to the patient's spine.

FIG. 9 shows an exemplary access status screen 110 utilized when asurgeon is accessing a patient's spine with a surgical accessory 20; theaccess status screen 110 having the mode section 60, the anestheticstatus section 72, the monitoring location status section 80, and anerve proximity screen 112 indicating that the surgical accessory 20 iswithin a predetermined range indicated as being an acceptable distanceaway from the patient's nerves and the other neural monitoringmodalities are indicated as being within a predetermined range of valuesindicating an acceptable reading.

The nerve proximity screen 112, in one embodiment, displays an amount ofcurrent needed to elicit a response from a nerve, in this case 14 mA. Itshould be noted that the nerve proximity screen 112 may also provideinformation with respect to the location of the nerve. In particular oneor more electrodes can be placed on a side of the surgical accessory 20.In this embodiment, rotation of the surgical accessory 20 will changethe location of the electrical stimulus to the patient and therebyprovide information with respect to the location of the nerve. In otherwords, the surgeon may rotate the surgical accessory 20 while monitoringthe nerve proximity screen 112 and then note locations where the currentneeded to elicit the response from the nerve is higher and lower andthen use this information to determine the location of the nerverelative to the surgical accessory 20.

FIG. 10 shows an exemplary access status screen 120 having the nerveproximity screen 112 issuing a warning to indicate that the surgicalaccessory 20 is within a predetermined range of values indicating thatthe surgical accessory 20 is an acceptable distance away from thepatient's nerves and/or other neural structures, but in close proximityto a vastus lateralis nerve and an anterior tibialis nerve. A warningcan be shown utilizing any suitable graphics, colors, sounds, smells orthe like. In this example, a warning is shown by utilizing a yellowhighlighted waveform window in the monitoring location status section 80as well as the yellow highlighting and lower current (7 mA) needed toelicit response from the nerve. In this case, the surgeon may want torotate the surgical accessory 20 while monitoring the nerve proximityscreen 112 to determine the location of the nerve relative to thesurgical accessory 20, and then retract and move the surgical accessory20 away from the nerve.

FIG. 11 shows an exemplary access status screen 124 which is similar tothe access status screen 120 depicted in FIG. 10 with the exception thatthe nerve proximity screen 112 of the access status screen 124 isissuing an alert due to the surgical accessory 20 being within apredetermined range of values indicating that the surgical accessory 20is an unacceptable distance away from the patient's nerves and/or otherneural structures and, in particular to the FIG. 11, an unacceptabledistance away from the vastus lateralis nerve and the anterior tibialisnerve. The alert is shown by way of example utilizing red highlightingand a lower current (3 mA) needed to elicit a response from the nerve.In this event, the surgeon may want to rotate the surgical accessory 20while monitoring the nerve proximity screen 112 to determine thelocation of the nerve relative to the surgical accessory 20, and thenretract and move the surgical accessory 20 away from the nerve.

FIG. 12 shows an exemplary dissecting status screen 130 which is similarto the system status screen 58, except that the mode section 60indicates that the surgeon system 10 is placed in the dissecting mode inwhich a surgical accessory 20 such as a retractor is being utilized bythe surgeon and showing that one of the multiple neural monitoringmodalities is within a predetermined range of values that isunacceptable and thereby indication that a possible intrusion of thevastus lateralis nerve, a biceps femoralis nerve, and the anteriortibialis nerve has occurred.

FIG. 13 shows an exemplary dissecting status screen 134 in which astatus summary section 66 of the multiple neural monitoring modalitiesindicates that the SSEP, MEP, TOF, and NCV are all within apredetermined range of values indicating that an acceptable readingwhile the EMG is indicating that it is within a predetermined range ofvalues indicating that an unacceptable reading is occurring, and amonitoring location status section 80 indicating that with respect toparticular nerves and/or other neural structures, the predeterminedvalues being interpreted are either acceptable or not acceptable andissuing a warning with respect to particular nerves where the readingsare falling within the predetermined range of values indicating such anunacceptable state.

FIG. 14 shows an exemplary dissecting status screen 136 which is similarto the dissecting status screen 134 except that all of the multipleneural monitoring modalities are indicated as being within apredetermined range of values indicating an acceptable reading.

FIG. 15 shows an exemplary trial/insertion screen 140 which is similarto the system status screen 58 which was previously described withreference to FIG. 3. The trial/insertion screen 140 indicates that allof the multiple neural monitoring modalities being monitored areindicated as being within a predetermined range of values indicating anacceptable reading.

FIG. 16 shows an exemplary supplemental/fixation status screen 142 whichis similar to the system status screen 58 which was previously describedwith reference to FIG. 3. The supplemental/fixation status screen 142indicates that all of the multiple neural monitoring modalities beingmonitored are indicated as being within a predetermined range of valuesindicating an acceptable reading.

FIG. 17 is a flow chart illustrating an exemplary surgical method 200for conducting a surgical procedure utilizing direct lateral approach tothe lumbar spine utilizing the surgical system 10 depicted in FIGS. 1and 2 according to the presently disclosed and claimed inventiveconcept(s), process(es), methodology(ies) and/or outcome(s). Thesurgical method 200 is provided with a preop and preparation section202, a dissection and access section 204, and an end plate preparationand implant section 206. In general, the surgical method 200 begins withthe preop and preparation section 202 and moves sequentially through thedissection and access section 204 and the end plate preparation andimplant section 206.

Initially, the surgical method branches to the preop and preparationsection 202 in which the peripheral nerve stimulation electrodes 19, themotor evoked potential stimulator 23, the EMG electrodes 34, the anodeelectrode 35 and the common electrode 37 are placed onto the patient asindicated by a block 210. Then, the processor 12 a of the control unit12 verifies that all of the peripheral nerve stimulation electrodes 19,the motor evoked potential stimulator 23, the EMG electrodes 34, theanode electrode 35, and the common electrode 37 (hereinafter referred toas “electrodes”) are positioned correctly and functioning correctly asindicated by a block 212. If the electrodes are functioning correctly,then the preop and preparation section 202 branches to a block 214, andif not, branches back to the block 210 to correct the positioning andfunctioning of the electrodes.

At the block 214, the processor 12 a provides an electrode verificationindicia (shown in FIG. 3, for example, as the “check marks” next to eachof the SSEP, MEP, TOF and EMG of the status summary section 66) onto thetouchscreen display 36 and shows an initial status of the neuralmonitoring modalities such as TOF, SSEP, MEP, and EMG. The processor 12a, then branches to the block 216 where the surgeon utilizing thesurgeon system 10 confirms that the neural monitoring modalities areacceptable. If so, then the processor 12 a receives input from thesurgeon and then branches to a block 218 to display the system statusscreen 58 onto the touchscreen display 36. If not, then the processor 12a receives input from the surgeon to branch to the block 210 where anyincorrect placement of the electrodes can be corrected.

The positioning mode is then selected on the touchscreen display 36, forexample, and then the patient is positioned on a table as indicated by ablock 220, preferably in a lateral decubitus position, and then abolster is placed underneath the patient's hip to aid in opening a spacebetween the patient's 12th rib and the patient's iliac crest. It is alsorecommended to flex the table to aid in opening the space between the12th rib and the iliac crest. The patient is then secured to the tablein this position.

The processor 12 a of the surgical system 10 receives input from theelectrodes and records baselines for certain of the neural monitoringmodalities, such as SSEP, and MEP as indicated by a block 224. The preopand preparation section 202 then branches to a block 226 where waveformsof the neural monitoring modalities are provided on the touchscreendisplay 36 by the processor 12 a as well as information regarding thedirection/proximity of nerves.

As indicated by a block 228, the processor 12 a of the surgical system10 then branches to the dissection and access section 204 where thewaveforms of the neural monitoring modalities are provided on thetouchscreen display 36 as well as the direction/proximity of nerves. Themode of the surgical system 10 is switched to the approach mode and thesurgeon verifies that all of the neural monitoring modalities areacceptable. The surgeon then locates a correct operative level and anincision location preferably utilizing fluoroscopic views and then makesan incision on the skin of the patient preferably targeting an anteriorthird of the intravertebral disc space as indicated by a block 230. Alongitudinal incision may be used if multiple levels will be fused. Oncethe skin incision is made and subcutaneous tissue is taken down, theoblique muscles of the abdomen should be visible. The surgeon separatesthe muscle fibers with blunt dissection utilizing either their finger ora probe and enters a retroperitoneal space as indicated by a block 232.The current status of all of the neural monitoring modalities isdisplayed and the surgeon reviews the touchscreen display 36 todetermine whether the position of the finger and/or the probe is safe ata block 234. If so, then the method branches to a step 236 to recordbaselines of certain of the neural monitoring modalities such as SSEPand MEP. If not, then the method branches to the block 232 where thesurgeon may retract the finger or the probe to try a different position.

The surgeon then switches the surgeon system 10 into the access mode,and the surgeon moves the peritoneum anterior with the forefinger or theprobe and continues blunt dissection to palpate down to a transverseprocess and slides forward to the psoas muscle. The surgeon then placesthe K-wire 25 or the dilator 26 through the psoas muscle to form aninitial access passageway to the patient's spine as indicated by a block238. The processor 12 a then utilizes one or more of the neuralmonitoring modalities such as a free run, NCV and/or a triggered EMG todetermine that the K-wire 25 or the dilator 26 are not interfering withany of the nerves and display the current status of the neuralmonitoring modalities on the touchscreen display 36 as indicated byblocks 240 and 242.

A series of dilators are then placed into the patient to enhance a sizeof the operative corridor as indicated by blocks 244, 246, 248, 250,252, and 254 and the current status of the neural monitoring modalities,such as free run, NCV and/or triggered EMG, is displayed on the touchscreen display 36 as well as a direction/proximity of nerves asdiscussed above preferably utilizing the access status screen 110 shownin FIG. 9, for example. The dilators can be either disposable orreusable. Further, the dilators may each include a single electrode, andbe formed of aluminum with an insulating coating. The dilators may alsoinclude multiple electrodes as discussed in more detail below withreference to FIGS. 18-20.

The method then branches to a block 256 where the surgeon system 10records baselines for the neural monitoring modalities such as SSEP, NCVand MEP and then provides the current status of the neural monitoringmodalities on the touchscreen display 36 preferably using the systemstatus screen 58 shown in FIG. 3 as indicated by a block 258.

The surgeon then switches the mode of the surgeon system 10 to thedissecting mode and places a retractor over the dilators as indicated bya block 260. The surgeon system 10 records baselines of the neuralmonitoring modalities such as SSEP, MEP and NCV as indicated by block262. The baselines of the neural monitoring modalities are provided onthe touchscreen display 36 and the surgeon determines whether thepatient's nerve health is acceptable at a block 264. If not, the methodbranches to the block 260 where the surgeon removes the retractor andthen replaces the retractor within the patient. Once a suitable positionfor the retractor is located, the retractor is preferably secured inthis position with a retractor clamp connected to the table, forexample. Once the retractor is secured, the surgeon expands theretractor as indicated at block 266 and then the surgeon system 10records baselines of the neural monitoring modalities such as SSEP, MEPand NCV at a block 268 and then displays the neural monitoringmodalities onto the touchscreen display 36. The surgeon again verifiesthat the patient's nerve health is acceptable in a block 270 to completethe dissection and access section 204.

The method 200 then branches to a block 274 where the waveforms of theneural monitoring modalities are displayed on the touchscreen display36. The surgeon verifies that the nerve health is acceptable and thenprepares the end plates of the patient's spine utilizing any suitabletools such as a curette and a rasp at a block 276. The surgeon thenplaces a trial spacer between the end plates as indicated by block 278,verifies the position of the trial spacer utilizing a fluoroscope forexample and then obtains responses from the neural monitoring modalitiessuch as SSEP, MEP and NCV as indicated by block 280. With respect toNCV, the responses of a segment of a nerve can be monitored with asurgical access instrument described in detail below with reference toFIGS. 18-20, or between an electrode at the surgical target site andanother electrode away from the surgical target site. The waveforms ofthe neural monitoring modalities are displayed on the touchscreendisplay 36 and the surgeon verifies that the patient's nerve health isacceptable at a block 282. If not, the method 200 branches to the block278 where the surgeon will then replace or move the trial spacer. Oncethe trial spacer is properly positioned and the patient's nerve healthis determined to be acceptable, then the trial spacer is removed and agraft is placed between the patient's end plates at a block 284. Thecurrent status of the neural monitoring modalities is displayed on thetouchscreen display 36 at a block 286 and the surgeon verifies that thepatient's nerve health is within acceptable predetermined ranges at ablock 288.

If the surgery will include supplemental fixation to provide support tothe patient's spine, then the surgeon will place the surgeon's system 10in the supplemental fixation mode. The current status of the neuralmonitoring modalities is displayed on the touchscreen display 36 whilethe surgeon connects appropriate hardware to the patient's spinepreferably using fluoroscopic techniques to monitor the exact locationof the hardware relative to the patient's spine. Common hardware forsupplemental fixation includes, but is not limited to, plates, rods andscrews that cooperate to provide supplemental support to the patient'sspine. If any of the neural monitoring modalities indicates that thehardware is within an unacceptable predetermined distance to any ofpatient's nerves or other neural structures, then the surgeon's system10 will issue an alert to the surgeon preferably through visual,olfactory or auditory methodologies. After the hardware is installed,then the surgeon may verify the relative location of the hardware usingfluoroscopic techniques, and use the screw test probe 32 to provide anelectrical medium to the hardware to obtain additional informationregarding the hardware's proximity to any of the nerves. Suchinformation will preferably be shown on the touchscreen display 36 withthe current status of the neural monitoring modalities to permit thesurgeon to verify that the patient's nerve health is within acceptablepredetermined ranges. Thereafter, the surgeon may remove the retractorand close the incision using any appropriate technique known to one ofordinary skill in the art.

Referring now to FIGS. 18 and 19, in one embodiment, the surgical system10 can be used to produce NCV measurements within a surgical target site298; or terminating or originating from the surgical target site 298. Toproduce NCV measurements in relation to the surgical target site 298,one of the surgical accessories 20 (shown in FIG. 1, for example) mayinclude a surgical access instrument 300 and/or at least one peripheralelectrode 299 positioned away from the surgical target site and on anerve path of a nerve. The surgical access instrument 300 has one ormore bodies 301 (with one body 301 being shown and discussed herein byway of example) having a proximal end 302, a distal end 304, and one ormore electrodes 306 on the body 301 near the distal end 304. Twoelectrodes 306 a and 306 b are shown in FIG. 18 by way of example. Thesurgical access instrument 300 is also preferably provided with a lead307 for each electrode 306 so that each electrode 306 can beindependently connected to a suitable source of a physical agent, suchas a port on the patient module 14. In the example shown, the surgicalaccess instrument 300 is provided with two leads 307 a and 307 b. Thesurgical access instrument 300 may be in the form of a probe, dilator,retractor, or any other suitable medical instrument, for example, solong as the surgical access instrument 300 is configured to be placed inthe surgical target site 298 and at least one electrode 306 ispositioned on or near the distal end 304 for contacting tissue that maycontain one or more nerves. The surgical system 10 may also be providedwith a ground electrode 308 to facilitate production of NCVmeasurements, as will be further discussed below.

The electrode 306 may be configured as a stimulating electrode to applythe physical agent to the surgical target site 298 to produce a neuralresponse in a nerve 310 that is proximate to the electrode 306. In otherwords, the term “proximate” means next to or on the electrode 306 so asto be stimulated and produce the neural response. The electrode 306 mayalso be configured as a recording electrode to measure the neuralresponse in the nerve 310 produced by the physical agent applied to thepatient by a stimulating electrode either at the surgical target site298 or elsewhere on a nerve path 314 of the nerve 310. The one or moreelectrode 306 may be partially embedded within the surgical accessinstrument 300 such that a portion of the one or more electrode 306remains exposed, may be connected via adhesive, may be formed fromflowable epoxy ink, or provided in any other suitable fashion, forexample. Where the surgical access instrument 300 is a retractor with abody 301 having one or more blades, the electrode 306 may be partiallyembedded in or placed on one of the one or more blades as previouslydescribed. Further, the one or more electrode 306 may be formed as apart of the body 301 by making the body 301 out of a first material,such as aluminum that is configured to pass the physical agent, and thencoating areas of the body 301 that may contact the tissue other than theone or more electrode 306 with a second material configured to block thephysical agent.

The one or more peripheral nerve electrodes 299 may be implementedsimilarly to the plurality of peripheral nerve stimulation electrodes19, the common electrode 37, the EMG electrodes 34, or the motor evokedpotential stimulator 23 described above with reference to FIG. 1. Theone or more peripheral nerve electrodes 299 may act as stimulatorelectrodes or recording electrodes for the purposes of NCV measurements.

In this embodiment, the surgical system 10 may produce NCV measurementsby placing the body 301 of the surgical access instrument 300 in asurgical target site 298 near the nerve 310. For example, the surgicaltarget site 298 may be located close to the common peroneal nerve fibersbetween spinal locations L-4-L-5 and S-1-S-2. It will be understood thatthe NCV measurements may also be used for the saphenous, genitofemoral,or any other nerve pertinent to a surgical procedure. The body 301 ofthe surgical access instrument 300 may be placed into tissue, such as apsoas muscle 312, proximate to the nerve 310, such as the peroneal nervefibers. The one or more peripheral nerve electrodes 299 may have beenplaced a predetermined distance from the surgical target site 309 andthe body 301 of the surgical access instrument 300 along the nerve path314 formed by the nerve 310, such as the peroneal nerve. The groundelectrode 308 may be placed between the surgical access instrument 300and the one or more peripheral nerve electrodes 299, but is preferablyless than 12 inches from the surgical target site 298. The one or moreelectrodes 306 and the one or more peripheral nerve electrodes 299 mayact as stimulating electrodes or recording electrodes along the nervepath 314 of the peroneal nerve, for example. The one or more electrode306 may also stimulate the nerve 310 allowing the one or more peripheralnerve electrodes 299 to receive electrical signals indicative of aneural response to the stimulation by the electrode 306, with the groundelectrode 308 serving to reduce artifacts within the electrical signalproduced along the nerve path 314. In this embodiment, the one or moreperipheral nerve electrodes 299 receiving the electrical signal allowthe surgical system 10 to monitor the nerve conduction velocity of thenerve 310, as described above in combination with the other neuralmonitoring modalities discussed above. Similarly, the one or moreperipheral nerve electrodes 299 may serve as stimulating electrodes andthe one or more electrode 306 may serve as the recording electrode. Abaseline NCV measurement may be taken at the beginning of the surgicalprocedure to establish a normal range of NCV for the patient. NCVmeasurements may occur at predetermined intervals or random intervalsduring a surgical procedure to ensure that the nerve conduction velocityof nerves 310 that could be affected by the procedure are within anormal range.

As shown in FIGS. 19 and 20, the surgical access instrument 300 may beprovided with two or more electrodes 306 a and 306 b. With regard toFIG. 19, electrodes 306 a and 306 b may be used to produce NCVmeasurements of a segment 315 of the nerve 310 adjacent to the surgicalaccess instrument 300 that is within the surgical target site 309. Theelectrodes 306 a and 306 b may be positioned at fixed locations andspaced apart a known distance 316.

The stimulation and recording can be conducted in a bipolarconfiguration or a monopolar configuration. In a bipolar configuration,the electrodes 306 a and 306 b are arranged to create the stimulationzone by at least one of the electrodes 306 a and 306 b applying thephysical agent to the segment 313 of the nerve, while another one of theelectrodes 306 a and 306 b is used to receive electrical signalsindicative of a neural response to the physical agent to produce NCVmeasurements. This bi-polar stimulation may be used where nerves and/orthe segment 315 are positioned near or between the electrodes 306 a and306 b. When using the bipolar configuration, the known distance 316 canbe varied based upon a number of factors including the size of theelectrodes 306 a and 306 b, as well as an amount of power used totransmit along the nerve 310. In one embodiment, the known distance 316can be within a range of 0.5 cm to 2 cm, to create a stimulation zoneencompassing the segment 315 of the nerve 310 adjacent to the surgicalaccess instrument 300. In a monopolar configuration, both of theelectrodes 306 a and 306 b may be used to apply the physical agent tothe segment 315 of the nerve 310, and the ground electrode 308, separatefrom the surgical access instrument 300, may receive electrical signalsindicative of a neural response to the physical agent. Alternatively, inanother monopolar configuration, both of the electrodes 306 a and 306 bcan be used to receive a neural response that is caused by stimulationof the nerve 310 from one of the peripheral electrodes 299. In thiscase, the electrodes 306 a and 306 b would receive the neural responseat different instants of time, e.g., times T1 and T2, respectively. Thedifference between the times T1 and T2, and the known distance 316 canbe used to measure the nerve conduction velocity of the nerve 310adjacent to the surgical access instrument 300. To use the monopolarconfiguration, the distance 316 can be in a range of 0.5 cm to 7.2 cm.

Using two monopolar electrodes 306 a and 306 b may be advantageous whenexcessive noise is present in the system due to biological electricalactivity. When used in a bipolar configuration, the electrodes 306 a and306 b may be more sensitive to the distance 316 and the power used.Also, a bipolar configuration may be more sensitive to localinnervation, but may have a narrower electrical measurement range. Thecontrol unit 12 may be programmed (e.g., provided with computerexecutable instructions) to permit the user to use either the monopolarconfiguration or the bipolar configuration as well as switch between themonopolar configuration and the bipolar configuration.

FIG. 20 shows another embodiment of a surgical access instrument 300 aconstructed in accordance with the present disclosure. The surgicalaccess instrument 300 a may be identical in construction and function asthe surgical access instrument 300 describes above, with the exceptionthat the surgical access instrument 300 a is provided with more than twoelectrodes 320. In the example shown, the surgical access instrument isprovided with four electrodes 320 a, 320 b, 320 c and 320 d that arearranged in a grid formation. However, more electrodes 320 can beprovided, and arranged in manners other than a grid formation.

The electrodes 320 a and 320 b; and 320 c and 320 d are spaced apartlaterally on a body 322 of the surgical access instrument 300 a adistance 324. The electrodes 320 a and 320 c; and 320 b and 320 d arespaced apart longitudinally on the body 322 a distance 326. Thedistances 324 and 326 can be the same or different, and such distances324 and 326 may be known so that the nerve conduction velocity can bedetermined. Further, the distance between any pair of the electrodes 320a-d may be known so that any two of the electrodes 320 a-d can be usedto measure the nerve conduction velocity. The plurality of electrodes314 a-314 b may be implemented and used similar to electrode 306 andelectrodes 306 a and 306 b. Nerve conduction velocities can bedetermined using various pairs of the electrodes 320 a-d. In thismanner, the surgical access instrument 300 a can be used to facilitateoptimal nerve alignment to the electrodes 320 a-d, as well as determinethe location and/or the direction of the nerve path 314 of the nerve 310relative to the location of the body 322 of the surgical accessinstrument 300 a. In other words, the electrodes 320 a-d may alsofacilitate optimal nerve alignment to the electrodes and be operated inpairs to perform NCV measurements.

The surgical access instrument 300 may also be used to generate anF-wave to measure NCV when the electrode 306, the electrodes 306 a and306 b, or the plurality of electrodes 314 a-314 d are in contact or neara motor nerve, in order to measure the NCV of the motor nerve.Additionally, the surgical access instrument 300 may generate an H-waveto stimulate a nerve and record a reflexive electrical discharge from amuscle in a limb, using the one or more peripheral nerve electrodes 299.The afferent impulse, the physical agent produced by the one or moreperipheral nerve electrodes 299, may occur in sensory nerves going froma limb to the spinal cord. An efferent impulse, the physical agentproduced by the surgical access instrument 300 may occur in motornerves.

One skilled in the art will recognize that the presently disclosedconcepts can be implemented in a variety of manners, such as systems,products, methods and/or kits of component parts grouped together and/orcapable of being assembled. For example, in one embodiment, the surgicalaccess instrument 300 or 300 a can be grouped together with the controlunit 12 and/or the patient module 14 to form a surgical system kit.

The preceding description has been presented with reference to someembodiments. Persons skilled in the art and technology to which thisdisclosure pertains will appreciate that alterations and changes in thedescribed structures and methods of operation can be practiced withoutmeaningfully departing from the principle, and scope of thisapplication. Accordingly, the foregoing description should not be readas pertaining only to the precise structures described and shown in theaccompanying drawings, but rather should be read as consistent with andas support for the following claims, which are to have their fullest andfairest scope.

Furthermore, none of the description in the present application shouldbe read as implying that any particular element, step, or function is anessential element which must be included in the claim scope. The scopeof patented subject matter is defined only by the allowed claims.Moreover, none of these claims are intended to invoke paragraph six of35 USC §112 unless the exact words “means for” are followed by aparticiple.

1-25. (canceled)
 26. A surgical system kit, comprising: at least twoelectrodes configured to be placed on a nerve path of a nerve within apatient, one of the electrodes configured to apply a physical agent andone or more other electrodes configured to receive a response from thepatient; one or more patient module configured to be connected to theelectrodes and configured to stimulate at least one of the electrodesand receive information indicative of a neural response from a segmentof the nerve from another one of the electrodes; and a control unitconfigured to be coupled to the one or more patient module, receive theinformation indicative of a neural response, and interpret theinformation according to a nerve conduction velocity modality todetermine the nerve conduction velocity of the segment of the nerve. 27.The surgical system kit of claim 26 wherein the at least two electrodescomprise a ground electrode, an electrode on a body of a surgical accessinstrument, and a peripheral electrode, wherein the ground electrode isconfigured to be placed between the surgical access instrument and theperipheral electrode.
 28. The surgical system kit of claim 26, whereinat least two of the electrodes are on a body of a surgical accessinstrument and spaced apart a distance of at least 0.5 cm, and whereinthe surgical access instrument is a dilator.
 29. The surgical system kitof claim 26, wherein at least two of the electrodes are on a body of asurgical access instrument and spaced apart a distance of at least 0.5cm, and wherein the surgical access instrument is a probe.
 30. Thesurgical system kit of claim 26, wherein at least two of the electrodesare on a body of a surgical access instrument and spaced apart adistance of at least 0.5 cm, and wherein the surgical access instrumentis a retractor, the retractor having one or more blades and wherein theelectrode is connected to one of the one or more blades.
 31. Thesurgical system kit of claim 26, wherein at least one of the electrodeis formed from a flowable epoxy ink.
 32. The surgical system kit ofclaim 26, wherein at least one of the electrode is partially embedded inthe surgical access instrument.
 33. The surgical system kit of claim 26,wherein the electrode is configured to generate an F-wave at thesurgical target site to measure nerve conduction velocity when the oneor more peripheral electrode stimulates a motor nerve.
 34. A surgicalsystem kit, comprising: a surgical access instrument configured to beplaced in a surgical target site and having a body with a proximal end,and a distal end, two or more electrodes on the distal end at fixedlocations and spaced apart a known distance, a first electrode of thetwo or more electrodes configured to apply a physical agent to a segmentof a nerve and a second electrode the two or more electrodes configuredto receive a neural response; and a control unit configured to, send asignal to the first electrode, receive the information indicative of aneural response from the second electrode, and interpret the informationaccording to a nerve conduction velocity modality to measure the nerveconduction velocity through the segment of the nerve.
 35. The surgicalsystem kit of claim 34, wherein the known distance is greater than 0.5cm.
 36. The surgical system kit of claim 34, wherein the surgical accessinstrument is a dilator.
 37. The surgical system kit of claim 34,wherein the surgical access instrument is a probe.
 38. The surgicalsystem kit of claim 34, wherein the surgical access instrument is aretractor, the retractor having one or more blades and wherein at leasttwo of the two or more electrodes are connected to the one or moreblades.
 39. The surgical system kit of claim 34, wherein at least one ofthe electrodes is formed from a flowable epoxy ink.
 40. The surgicalsystem kit of claim 34, wherein at least one of the electrodes ispartially embedded in the surgical access instrument.
 41. The surgicalsystem kit of claim 34, further comprising one or more patient moduleconfigured to be connected to the surgical access instrument, transmit asignal to one of the two or more electrodes, and receive informationindicative of the neural response from another one of the two or moreelectrodes.
 42. The surgical system kit of claim 41, wherein the controlunit further comprises a base, and wherein at least one of the patientmodules is within the base.
 43. A surgical system kit, comprising: aperipheral electrode; a surgical access instrument configured to beplaced in a surgical target site and having a body with a proximal end,and a distal end, two or more electrodes on the distal end at fixedlocations and spaced apart a known distance; and a control unitconfigured to, send a signal to the peripheral electrode, receive theinformation indicative of a neural response from at least one electrodeof the surgical access instrument, and interpret the informationaccording to a nerve conduction velocity modality to measure the nerveconduction velocity through the segment of the nerve.
 44. The surgicalsystem kit of claim 43, wherein the known distance is greater than 0.5cm.
 45. The surgical system kit of claim 43, wherein the surgical accessinstrument is a dilator.
 46. The surgical system kit of claim 43,wherein the surgical access instrument is a probe.
 47. The surgicalsystem kit of claim 43, wherein the surgical access instrument is aretractor, the retractor having one or more blades and wherein at leasttwo of the two or more electrodes are connected to the one or moreblades.
 48. The surgical system kit of claim 43, wherein at least one ofthe electrodes is formed from a flowable epoxy ink.
 49. The surgicalsystem kit of claim 43, wherein at least one of the electrodes ispartially embedded in the surgical access instrument.
 50. The surgicalsystem kit of claim 43, further comprising one or more patient moduleconfigured to be connected to the surgical access instrument, transmit asignal to one of the two or more electrodes, and receive informationindicative of the neural response from another one of the two or moreelectrodes.
 51. The surgical system kit of claim 50, wherein the controlunit further comprises a base, and wherein at least one of the patientmodules is within the base.
 52. The surgical system kit of claim 43,wherein the control unit is configured to receive the informationindicative of the neural response from at least two electrodes of thesurgical access instrument at different instants of time, and interpretthe information according to a nerve conduction velocity modality usinga time difference between the different instants of time and the knowndistance in which the two or more electrodes are spaced apart.